How to FSCK root booting from CD

[Fernando Cassia]

Something as FSCK´ing the boot partition is giving me the fits.

If I boot from the hard disk as root in single user mode, and attempt
to fsck root, I get a warning about causing irreversible damage to the
filesystem by checking an ACTIVE volume.

If I boot from CD and start recovery mode to a command prompt, when I
attempt to mount the Volgroup00 I get a message about not finding
/dev/fstab.

So WHAT is the right procedure for doing a fsck in the boot volume?.

I´ve been hit months ago by the dreaded "Can´t write to volume, disk
full" bug while doing automatic system updates and I´ve been unable to
boot to a graphics desktop ever since. I tried erasing several 700MB
CD images and 4GB DVD images yet if I df -H I continue seeing 100%
filesystem usage.

Thanks in advance,
FC